Many applications of microwave (1-30 GHz) and millimeter wave (30-300 GHz) technology use either solid-state or vacuum-tube components to generate or amplify the microwave or millimeter-wave signals. The applications for microwave and millimeter-wave technology often require output powers that are higher that the power that can be generated by a single component. Because the output power of a single amplifying element is often not strong enough, the outputs of many amplifying elements must be combined. One method of power combining several devices is to use a probe-fed waveguide launch (i.e., a waveguide probe) that is coupled to one or more power amplifiers and generally launch or direct an amplified wave into a waveguide. In this case, conventional waveguide designers have combined multiple probes in one waveguide to combine the power amplification of each probe and to propagate a high powered wave signal.
This conventional power combining technique includes combining the output power from multiple power amplifiers in a waveguide via corresponding probes which are identical in terms of size, material used, the depth of each probe, etc. Because a power combiner generally achieves best performance when all power amplifiers and corresponding probe launches contribute equally to form a combined power wave signal, conventional power combiners employ symmetry in positioning each probe within the waveguide. In other words, a combined wave signal performs best ideally when each amplifier coupled to each corresponding probe is saturating at the same time, and in conventional combiners, each probe is symmetrically positioned in the waveguide in such a way to achieve this end.
As an example of each probe contributing equally to the combined power wave signal, FIG. 1a illustrates a longitudinal cross section (i.e., side view) diagram and FIG. 1b illustrates a lateral cross section (i.e., end view) diagram of a conventional transmitter that includes an input waveguide 101, four identical amplifiers 110, four corresponding identical probes in the input waveguide coupled to the input terminals four amplifiers 110 via a corresponding coaxial cable 131 and symmetrically positioned from each probe in one plane that is disposed orthogonally to the direction of energy propagation 141, and four corresponding identical probes 122 in the output waveguide 102 coupled to the output terminals four amplifiers 110 via a corresponding coaxial cable 130 and symmetrically positioned from each other probe in one plane that is disposed orthogonally to the direction of energy propagation 142. In this example, the performance of the aggregate collection of amplifiers is optimized because each identical probe (and corresponding amplifier) is equally receiving power from the input wave, and equally contributing power to the output wave. This input and output equality is a result of the symmetrical positioning of the probes, as shown in FIG. 1. There are other examples of prior attempts with multi-probe based power combiners where equal power distribution among the probes is enforced by the symmetry of the structure
However, if each amplifier does not equally saturate relative to other amplifiers (e.g., because each probe is not symmetrically positioned relative to other probe), inefficiencies, such as loss of power level, energy waste, etc. are present. As an example of some of these asymmetries, as shown in the side view diagram of FIG. 2, a conventional power combiner that includes four amplifiers 110; an input waveguide 101; an output waveguide 102; four corresponding identical input probes 121 in the input waveguide, with each probe is coupled to the input of its respective amplifier; and four corresponding identical output probes 122 in the output waveguide, with each probe is coupled to the output of its respective amplifier. In this example of FIG. 2, each set of these four conventional identical input 121 and output 122 probes are disposed in two planes i) orthogonal to the direction of energy propagation 141 142 (i.e., the direction of the “Output” or “Input” arrow or the longitudinal axis of the waveguide) within the waveguide and ii) parallel to the electric field 151 152 (i.e., “E” arrow). Moreover, as illustrated in FIG. 2, one set of two input probes are situated in a plane that is positioned one quarter wavelength of a wave signal from a back wall 161 of the input waveguide (i.e., the opposite end of the waveguide opening). The other set of two input probes are situated in a plane that is positioned one half wavelength of a wave signal from the first set of two input probes (i.e., three quarters wavelength of a wave signal from a back wall of the waveguide). The same is true of the two sets of two output probe 122s. As a result of this conventional configuration of FIG. 2, the power output from all four amplifiers 110 are combined in the waveguide along the direction of energy propagation.
However, because the two sets of two input probes 121 in FIG. 2 are disposed in a differently located planes orthogonal to the direction of energy propagation 141 within the input waveguide 101 (i.e., the probes are not symmetrically positioned to one another), the power being received from the input waveguide by each amplifier (and corresponding coupled input probe) is not equally driving each amplifier. In addition, the two sets of two output probes 122 in FIG. 2 are disposed in a differently located planes orthogonal to the direction of energy propagation 152 within the output waveguide 102 (i.e., the probes are not symmetrically positioned to one another), the power launched into the output waveguide 102 from each amplifier 110 (and corresponding coupled probe) is not equally contributing power to the overall combined output wave signal. These effects at the input side and the output side will mean that the amplifiers are not saturating at the same time, resulting in power inefficiencies. Because the input 121 and output 122 probes, as shown in FIG. 2, are of equal size, set at equal depth, constructed of the same material, etc. and only differ in being located at two different planes within the waveguide, neither the input amplitude coupling (i.e., energy transferred from the input waveguide to the input probe) among the four input probes 121 nor the output amplitude coupling (i.e., energy transferred from the output probe to the output waveguide) among the four output probes 122 are not sufficiently similar or are not equalized.
As another example that suffers from unequal power contribution among the input and output probes, FIGS. 3a-3c illustrate diagrams of another conventional transmitter that includes three identical input probes 121 symmetrically disposed in the input waveguide 101 in one plane orthogonal to the direction of energy propagation 141. Similarly, there are three identical output probes 122 symmetrically disposed in the output waveguide 102 in one plane orthogonal to the direction of energy propagation 142. Despite the fact that the three input probe launches 121 and three output probe launches 122 are symmetrically positioned, as illustrated in FIGS. 3b-3c, the electric field intensity 201 is not uniform over the cross section but sinusoidal in form (i.e., strongest intensity levels in the center of the input and output waveguide and tapering off to zero at the edges of the cross section of the input and output waveguide.) Because each input probe 121 in this three-way combiner is identical, as illustrated in FIG. 3b, the two flanking input probes excite the corresponding amplifier 110 differently than the central input probe as opposed to a more desired uniform distribution of power among the three amplifiers. Similarly, because each output probe in this three-way combiner is identical, as illustrated in FIG. 3c, the two flanking output probes couple to the output signal differently than the central output probe as opposed to a more desired uniform distribution of power among the three amplifiers 110.